圆管中激光激发表面瑞利波极性的有限元分析

用有限元方法数值模拟了脉冲线源激光作用于厚铝管时产生的温升以及由此温升而产生的表面声波的情况,得到了逆时针向探测点和波源之间角度从=5°到=180°范围内一系列表面法向位移的时域波形,并对相同厚度不同外径的铝管的表面波进行对比。数值结果表明表面声波中显著的波为掠面纵波、头波和瑞利波,第一个瑞利波脉冲的极性在传播过程中发生了倒转现象,逆时针向看探测点离波源的角度,当较小时瑞利波脉冲是单极性的(负的),随着角度的增大,瑞利波脉冲逐渐变为双极性的,且双极性中正向极性逐渐增大,到=90°时变为完全双极性(正向和负向对称)。随着角度的进一步增加,双极性中负向极性逐渐减小,到=180°时瑞利波脉冲又变为单极性(正的)。不考虑衍射效应时,圆管中第一个瑞利波脉冲的极性和试样的尺寸无关,仅和探测点离波源的角度相关。     

Linear hydraulic pressure-pulse actuator (LHPA): a versatileinstrument that produces a simulated blood pressure pulse wave for smallsized vessels

An instrument is presented which produces a simulated circulatory pulsatile pressure wave for small sized vessels. The linear hydraulic pressure-pulse actuator (LHPA) is designed to be extremely versatile, that is, a blood pressure wave source of any shape, amplitude, offset and frequency can be simulated. In addition, the LHPA can reproduce accurately a real pulse pressure wave by simply inputting an actual data record of a circulatory pressure pulse. The design is accomplished by incorporating the use of a linear force solenoid driven with a voltage-to-current source power amplifier. Testing of the device is presented here, as well as pressure pulse results from a recorded pulsatile pressure input to the LHPA. The device is simple to implement in that its response is linear, for volume changes upto ±5 mL, without the need for feedback compensation     

Predicting arterial stiffness from the digital volume pulse waveform

Cardiovascular disease (CVD) is currently the biggest single cause of mortality in the developed world, hence, the early detection of its onset is vital for effective prevention therapies. Aortic stiffness as measured by aortic pulse wave velocity (PWV) has been shown to be an independent predictor of CVD, however, the measurement of PWV is complex and time consuming. Recent studies have shown that pulse contour characteristics depend on arterial properties such as arterial stiffness. This paper presents a method for estimating PWV from the digital volume pulse (DVP), a waveform that can be rapidly and simply acquired by measuring the transmission of infra-red light through the finger pulp. PWV and DVP were measured on 461 subjects attending a clinic in South East London. Techniques for extracting features from the DVP contour based on physiology and information theory were compared. Low and high stiffness were defined according to a threshold level of PWV chosen to be 10 m/s. Using a support vector machine-based classifier, it is possible to achieve high overall classification rates on unseen data. Further, the use of support vector regression techniques lead to a direct real-valued estimate of PWV which outperforms previous methods based on multilinear regression. We, therefore, conclude that support vector machine-based classification and regression techniques provide effective prediction of arterial stiffness from the simple measurement of the digital volume pulse. This technique could be usefully employed as a cheap and effective CVD screening technique for use in general practice clinics.     

Statistical amplitude and phase variations in mode-locked lasers

The influence of statistical amplitude or phase variations in the modes of a mode-locked laser on the time-dependent output intensity and on the relative efficiency of nonlinear optical processes is investigated. The ensemble-averaged intensity, the time-dependent distribution of the resulting complex amplitude, and the second-order moment of the intensity distribution are calculated and discussed for both types of variations. As long as no systematic amplitude or phase changes are introduced, the pulse shape is maintained, but superimposed on a fluctuating background, and the efficiency for nonlinear optical processes is reduced. For random phase fluctuations over 2π the pulse behavior disappears completely and the output becomes Gaussian or chaotic light.     

基于脉搏波速法的动态血压测量系统设计

提出一种利用脉搏波传导速度法的血压测量方案。采用新型可穿戴式光电传感器分别采集人体左侧桡动脉和指端的脉搏波,摆脱传统袖带式的测量方式。通过分析脉搏波的波形,计算脉搏波传导速度,建立数学模型方程,对非侵入式的动态血压测量进行研究,并采用听诊法进行校准和误差分析,实现连续血压测量。实验结果表明,该系统测量方便,精度较高,与听诊法具有良好的一致性。     

A new oscillometry-based method for estimating the brachial arterial compliance under loaded conditions

We propose a new method for assessing the compliance of a compressed brachial artery using an oscillometry-based approach that is mathematically based on artery and air-cuff models. The cuff dynamics during the inflation period were characterized by simultaneously recording the cuff volume and internal pressure with a pressure transducer and an airflow meter, respectively, which yielded the envelope of the oscillation amplitudes (OAs) in the air cuff. This allowed the change in the arterial volume during each heartbeat at different cuff pressures to be calculated, yielding a changed volume-pressure curve. The oscillometry-derived loaded compliance of the brachial artery ( C _osci) can be determined as the dynamic changed volume divided by the pulse pressure. Furthermore, we developed a direct scheme to calibrate the calculated dynamic changed volume. In addition, the proposed C _osci was validated by comparing it with the compliance of the brachial artery (C _echo ) estimated echocardiographically from the brachial arterial blood flow in 32 patients whose lower limbs exhibited numbness or lack of strength. The results showed that C _osci and C _echo were significantly correlated between the cuff pressures levels and the mean arterial pressure, systolic pressure, and diastolic pressure ( r = 0.616, 0.571, and 0.666, respectively; p < 0.0001). This suggests that a useful measure of the loaded compliance can be derived from the pattern of the OA waveform in addition to oscillometry-based blood pressure measurements.     

Noninvasive Measurement of the Volume Elastic Modulus in Finger Arteries Using Photoelectric Plethysmography

A method for the nonivasive measurement of the volume elastic modulus (Ev) in human finger arteries was developed. The volume change ratio and pulse pressure in the arteries were simultaneously determined by a transmittance type infrared photoelectric plethysmograph and a volume oscillometric sphygmomanometer using an occlusive cuff. The Ev values could be obtained at a desired transmural pressure level of the arteries which was controlled by the cuff. A clear difference was revealed between the Ev values obtained in the fingers of two male subjects of 33 and 65 years old. The values determined by this method were compared to those calculated from pulse wave propagation velocity (Evp) obtained simultaneously in the fingers of 11 subjects. The linear regression equation was Ev = 1.31 Evp ?0.117 with a correlation coefficient r = 0.893 (n = 39). These results suggest that this should be a useful and noninvasive method of evaluating changes in arterial elasticity accompanying aging and perhaps influenced by accompanying hypertension or arteriosclerosis.     

Magnetostatic correlator of microwave signals with the internal wave front reversal

A new technique of the correlation processing of data based on the nonlinear interaction of signals of backward volume magnetostatic waves in yttrium-iron garnet thin films and a corresponding laboratory mock-up of the correlation receiver operating in the 6 cm wavelength range have been presented in this paper. It was proposed to use additional pumping pulse for obtaining a time-reversed signal pulse. The resultant correlation signal occurred during the nonlinear interaction of the delayed signal wave and the pumping-reversed wave. The specificity of the passage of broadband signals through the resonance system of waveguide of spin waves was taken into account. It has been found out that the resonance properties of the correlator affect the efficiency of the desired signal separation from the noise level. The resultant signal-to-noise ratio for the output signal was enhanced by more than 20 dB.     

Pulse Dynamics of Flexural Waves in Transformed Plates

Coordinate-transformation-inspired optical devices have been mostly examined in the continuous-wave regime: the performance of an invisibility cloak, which has been demonstrated for monochromatic excitation, is likely to deteriorate for short pulses. Here, pulse dynamics of flexural waves propagating in transformed plates is investigated. A practical realization of a waveshifter and a rotator for flexural waves based on the coordinate transformation method is proposed. Time-resolved measurements reveal how the waveshifter deviates a short pulse from its initial trajectory, with no reflection at the bend and no spatial and temporal distortion of the pulse. Extending the strategy to cylindrical coordinates, a wave rotator is designed. It is demonstrated experimentally how a pulsed plane wave is twisted inside the rotator, while its wavefront is recovered behind the rotator and the pulse shape is preserved, with no extra time delay. The realization of the dynamical mirage effect is proposed, where an obstacle appears oriented in a deceptive direction.     

Optimal pulse shape for estimating positions of superimposed pulses

In this correspondence, we determine the optimal pulse shape for estimating positions of superimposed pulses by deriving the Cramer-Rao lower bound (CRLB) on the average estimation error variance and numerically optimizing it with respect to pulse shape. Our results show that a significant improvement in estimation error variance can be achieved relative to Gaussian and rectangular pulse shapes     

Noninvasive measurement of compliance of human leg arteries

Electrical impedance plethysmography has been evaluated for early detection of peripheral atherosclerosis. A pressure cuff was wrapped around the lower leg and the cuff pressure increased. Two circumferential electrodes glued in the middle of the cuff recorded the impedance pulse, from which the arterial pulse volume was calculated. The ratio of maximal arterial volume change to the pulse pressure was determined as a measure of maximal compliance Cp. Based on the data from 118 human subjects, Cp was found to correlate well with known cardiovascular risk factors. For example, Cp decreased on the average from 3.08 to 1.92 microL.mm Hg-1.cm-1 (1 microL.mm Hg-1.cm-1 = 7.5 x 10(-10) m4.N-1) in groups of subjects of increasing age from 22 to 70 years. Subjects on a regular exercise program had an average value of 3.86, while those with proven peripheral vascular disease had a value of 0.70. In a related pathologic validation study on 15 monkeys fed a cholesterol-control diet a good correlation was found between the limb peak compliance and morphometric data obtained from iliac and carotid arteries.     

A Microcprocessor-Based Noninvasive Arterial Pulse Wave Analyzer

A microprocessor-based noninvasive arterial pulse wave analyzer is described which detects the peripheral, arterial pulse of an individual and extracts from the pulse waveform clinically important features. Continuous-wave Doppler microwaves (24.125 GHz) are employed to measure the arterial wall movements associated with the pressure pulse wave. Through the use of feature extraction techniques, key landmarks are located on the pulse contour. Then the pulse rate, the foot-to-systolic peak time period, and the foot-to-dicrotic notch time period are calculated. Preliminary results are presented which indicate that the arterial pulse wave analyzer can accurately determine the movement of the arterial wall and is able to analyze the pulse wave contour for clinically important features.     

Possible determinants of pulse-wave velocity in vivo

The relationship between arterial pulse-wave velocity and the possible factors (age, gender, blood pressure, heart rate, serum lipids, and disease state) involved were examined for 127 subjects using multivariate analysis. Since a preliminary study had shown that age correlated highly with transmission time of pulse waves rather than with their velocity, the former was used in this analysis. Transmission time was obtained from the transit time between fingertip-pulse and toetip-pulse waves, as estimated from the delay of the initial rise of pulse waves and from the delay of each of the six frequency components less than 7 Hz obtained with Fourier analysis. Multiple regression analysis indicated that the possible determinants of the transmission time were age, gender, systolic and diastolic blood pressures, and phospholipid     

Frequency analysis of the peripheral pulse wave detected in thefinger with a photoplethysmograph

A photoelectric plethysmograph is described that performs a frequency analysis of the peripheral volume pulse wave using a portable computer. It was used to determine how the pulse shape varied with age using 54 subjects in three age groups, 10-29, 30-59, and 60-89 years. The youngest group had a larger power in the second harmonic, (normalized to the fundamental), with p less than 0.05 than the older two groups. The decrease of power in the harmonics of the peripheral pulse wave with age may be a useful noninvasive measure of aging and vascular disease.     

Numerical simulations of light scattering by red blood cells

Scattering of electromagnetic waves from a red blood cell is simulated using the finite-difference time-domain method (FDTD), the Rytov approximation and the discrete dipole approximation (DDA). Both FDTD and DDA are full wave methods that give accurate results in a wide range of wavelengths. The Rytov approximation is a much simpler method that is limited to scattering angles within 30 degrees from the forward direction. The investigation comprehends different wavelengths and different orientations of the cell. It shows that the shape, volume, and orientation of the cell have a large influence on the forward scattering.     

Full-wave analysis of an infinitely long magnetic surface wavetransducer

A rigorous analysis of an infinitely long microstrip line embedded in a multilayer structure which includes a ferrite layer is presented. In certain frequency ranges, such a line launches magnetic surface waves in the ferrite layer and thus becomes a surface wave transducer. The analysis is a self-consistent, full-wave solution which rigorously includes the effect of radiating magnetic waves. By expanding the transducer currents in terms of both even and odd functions, it is shown that the principal current is not symmetrically distributed across the transducer width. The propagation constant of the transducer mode is complex and shows a large, imaginary part (attenuation) tied to the excitation of magnetostatic surface waves. In addition, the propagation constant remains complex even for frequencies above the magnetostatic surface wave bandwidth because the excitation of magnetic surface waves has complex propagation constants. Insertion loss measurements of a multilayer microstrip transducer are in reasonable agreement with the calculated attenuation     

Flexible Polymer Transducers for Dynamic Recognizing Physiological Signals

Ferroelectric polymers are of interest as most promising electroactive materials. Flexible transducers from ferroelectric polymer thin film with underneath semiconducting polymer active layer for high sensitive and versatile detection of physiological signals are described. When attached directly on the wrist, the flexible transducers can distinguish the transient pulse waves non‐invasively and in situ, due to their fast response (milliseconds) and high sensitivity (down to several Pascal) to instantaneous change of blood pressure. High‐resolution picture of one pulse wave is available to provide two most common parameters for arterial stiffness diagnosis. The transducers are also suitable for dynamic recognizing physiological signals under both physical exercise and medicine treatment, demonstrating their enormous potential for warning the risk of cardiovascular disease, and evaluating the efficacy of heart medicines. The transducers are easy to carry around with an operating voltage of 1 V and the power consumption less than 1 μW. Thus, they are valuable for applications like electronic skin and mobile health monitoring.     

A cardiac hypothesis for the origin of EEG alpha

Major hypotheses for the origin of EEG alpha suggest a neural basis, but omit to consider other electrical and mechanical aspects. A cardiac electromechanical hypothesis is proposed. This hypothesis suggests that the natural mechanical frequency of the skull-brain mass is approximately 10 Hz. This has been determined by model and direct measurement. Membrane, liquid junction, electrode, and static charges exist as nonneural sources of potential in EEG recording. These standing potentials can be modulated by pressure and movement. It is postulated that the arterial pulse shocks the brain mass into oscillation at its natural frequency modulating the nonneural potentials. The arterial pulse has a jitter as great as ±720 electrical degrees at 10 Hz and amplitude jitter of approximately ±10 mmHg. Because of cardiac jitter, the differential aspect of amplification, and mixing of waves in the skull, coherence of alpha with phase of the cardiac cycle could not be demonstrated. The cardiac electromechanical hypothesis may assist others in designing experiments that will establish a valid explanation for the origin of EEG alpha.     

Soliton shape stabilization in a superlattice with next-to-nearest neighbor spectrum in a field of a nonlinear wave

The effect of an electric field of a nonlinear (cnoidal) electromagnetic wave (pumping field) upon the shape of the solitary electromagnetic wave (soliton) in the quantum semiconductor superlattice with two harmonics of the electron spectrum is studied. Propagation of electromagnetic waves is shown in this case to be described by the modified double sine-Gordon equation. The possibility of the amplification of the pulse and its transformation into the dissipative soliton is noticed. The speed and width of a soliton depend on the presence of the second harmonic in the superlattice electron energy spectrum. The dependence of the dissipative soliton parameters on temperature and pumping field amplitude is also noticed. The possibility of propagation of electromagnetic waves described by solutions of the modified sine-Gordon equation in the superlattice with the spectrum under study is found.